Connectors that are used to align two optical fibers are commonly referred to as optical connectors. The vast majority optical connectors are of the “physical contact (PC)” type, and are referred to as PC optical connectors. In a PC optical connector that is used to connect two fibers, the two fibers are physically touching under pressure. For single mode fibers, the glass optical core of the fiber has to be aligned extremely accurately to ensure a low loss connection. This small core means that a scratch or dust on a fiber will cause the light to be greatly attenuated and potentially for the communication link to be lost
Another type of optical connectors is the “expanded beam” (EB) optical connector. An EB optical connector reduces the effect of dust contamination or scratches by using a lens or a pair of lenses to focus the light between the two optical fibers. Typically, EB optical connectors use alignment inserts to align the optical paths between opposing lenses of counterpart EB optical connectors. These alignment inserts are typically machined from metal blocks containing a number of cylindrical holes. Each lens is placed in one end of a corresponding hole, and the fiber and ferrule combination are placed into the other end of the corresponding hole. The alignment method combines face alignment with an alignment pin. These designs are common, and for example, MIL-PRF-83526 describes this connector style. This type of EB connector is also described in the following patents and published applications: U.S. Pat. No. 8,824,841, U.S. Patent Pub. No. 2007/0211999, U.S. Pat. Nos. 7,722,261, and 8,556,521. This type of EP optical connector may be known as an alignment insert exposed lens EB connector.
Another type of EB connector uses a single lens and a ferrule with the lens on one end of a tube and the fiber entering the other end. This type of EB connector also uses an alignment sleeve (commonly called split sleeve), in which the fiber, the lens, the ferrule, and the alignment tube are generally concentric. The light beam may or may not be concentric. Examples of these EB connectors are described in U.S. Pat. Nos. 8,244,084, 7,775,725, 8,827,567. This type of EB optical connector may be known as an alignment sleeve exposed lens EB connector.